[R-sig-Geo] rainfall interpolation using ANN

[ping yang]

Hi Nahm Lee and R-sig-geo,

I am quite interested in the IDW interpolation comparing to other methods
such as Krige, I have a code like this which I think also did the IDW:

library(gstat)
library(maptools)
library(raster)
dat71 <- readShapePoints("d:/FireDanger/IDW/71stations.shp")
bubble(dat71,"VALUE1")
sample.grid <- raster("rawsd_71Stations.tif")
Left <- bbox(sample.grid)[1]
Right <- bbox(sample.grid)[3]
Bottom <- bbox(sample.grid)[2]
Top <- bbox(sample.grid)[4]
cell.size <- res(sample.grid)
grid.xy <- expand.grid(x = seq(Left, Right, cell.size[1]), y = seq(Top,
Bottom, -cell.size[2]))
coordinates(grid.xy) <- ~x + y
gridded(grid.xy) = TRUE
value71.idw <- krige(VALUE1 ~ 1, dat71, grid.xy)
spplot(value71.idw["var1.pred"])
r_grid71 <- raster(value71.idw["var1.pred"])
plot(r_grid71)

However, I am not sure it is correct. Have someone using this method to do
the IDW? and One more question, How can I complete a Krige application
based on a shapefile (there are other examples using the spreedsheet).

Looking forward to hearing from you.

Peter

On Mon, Dec 1, 2014 at 12:31 PM, Nahm Lee <nlee at valleywater.org> wrote:

>  This is my example with idw based on a web site, #
> http://www.geo.ut.ee/aasa/LOOM02331/R_idw_interpolation.html.
>
>
>
> Nahm Lee
>
> nlee at valleywater.org
>
>
>
>
>
>
>
> # http://www.geo.ut.ee/aasa/LOOM02331/R_idw_interpolation.html
>
>
>
> library(ggplot2)
>
> library(gstat)
>
> library(sp)
>
> library(maptools)
>
> library(rgeos)
>
>
>
> setwd("C:/Users/Michael/Dropbox/R/SHP")
>
>
>
> AlertRain <- read.csv(file = "AlertRain.csv",header = TRUE)
>
>
>
> names(AlertRain)
>
>
>
> AlertRain_test <- AlertRain   # duplicate air temp. data file
>
> AlertRain$x <- AlertRain$longitude  # define x & y as longitude and
> latitude
>
> AlertRain$y <- AlertRain$latitude
>
>
>
> # Set spatial coordinates to create a Spatial object:
>
> coordinates(AlertRain_test) = ~x + y
>
>
>
> plot(AlertRain_test)
>
>
>
> # Define the grid extent:
>
> #x.range <- as.numeric(c(21.76, 28.21))  # min/max longitude of the
> interpolation area
>
> #y.range <- as.numeric(c(57.45, 59.72))  # min/max latitude of the
> interpolation area
>
>
>
> x.range <-
> c(min(round(AlertRain_test$x,2)-0.1),max(round(AlertRain_test$x,2)+0.1))
>
> y.range <-
> c(min(round(AlertRain_test$y,2)-0.1),max(round(AlertRain_test$y,2)+0.1))
>
>
>
> # Create a data frame from all combinations of the supplied vectors or
> factors.
>
> # See the description of the return value for precise details of the way
> this is done.
>
> # Set spatial coordinates to create a Spatial object. Assign gridded
> structure:
>
> grd <- expand.grid(x = seq(from = x.range[1], to = x.range[2], by = 0.1),
> y = seq(from = y.range[1],
>
>     to = y.range[2], by = 0.1))  # expand points to grid
>
> coordinates(grd) <- ~x + y
>
> gridded(grd) <- TRUE
>
>
>
> #Plot the weather station locations and interpolation grid:
>
> plot(grd, cex = 1.5, col = "grey")
>
> points(AlertRain_test, pch = 1, col = "red", cex = 1)
>
>
>
> # interpolate surface and fix the output:
>
>
>
> idw <- idw(formula = Elevation ~ 1, locations = AlertRain_test,
>
>     newdata = grd)  # apply idw model for the data
>
> ## [inverse distance weighted interpolation]
>
>
>
> idw.output = as.data.frame(idw)  # output is defined as a data table
>
> names(idw.output)[1:3] <- c("long", "lat", "var1.pred")  # give names to
> the modelled variables
>
>
>
> #Plot the results:
>
>
>
> ggplot() + geom_tile(data = idw.output, aes(x = long, y = lat, fill =
> var1.pred)) + scale_fill_gradient(low = "cyan", high = "orange")+
>
>     geom_point(data = AlertRain, aes(x = longitude, y = latitude), shape =
> 21,
>
>         colour = "red")+labs(title = "Elevation by rainfall station
> elevation")
>
>
>
>
>
>
>
> *From:* R-sig-Geo [mailto:r-sig-geo-bounces at r-project.org] *On Behalf Of *Mengxi
> Yang
> *Sent:* Monday, December 01, 2014 1:32 AM
> *To:* r-sig-geo at r-project.org
> *Subject:* [R-sig-Geo] rainfall interpolation using ANN
>
>
>
> Dear list,
>
> I am going to do daily rainfall interpolation using ANN. but I am not
> familiar with it. Can somebody give some advise or example?
>
>
>
> my data like:
>
>  I have 325 stations in different location.each station have unique code
> and coordinates. And I want to interpolate in 1km resolution. I have the
> mask map of NL.
>
> [image: Inline image 2]
>
>
>
> can someone give me some advice? because I want to compare ANN with
> Kriging and IDW.
>
> Thank you very much.
>
>
>
> Mengxi Yang
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
>
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